Low-speed tunnel tests were made on the Supermarine N 9/47 to check the effects of the jet flow on the longitudinal stability and to test the V-tailplane. A 1/5-scale model of the aircraft was used. The tests were made in the 11 1/2- by 8 1/2-ft tunnel with wind speeds of 80 and 120 fps, giving Reynolds numbers of 0.82 and 1.23 x 10 to the 6th power based on the standard mean chord of the wing. Modifications to the jet exit fillet increased its effectiveness in keeping the jet flow clear of the rear fuselage. The estimates of the over-all effect of the jets on the longitudinal stability agreed reasonably well with the measured values.